i can't find this part number in my Chevy parts book!!! So what does it fit , -3973456 flywheel 168 tooth.
That number is a casting number, not a part number, which is probably why you couldn’t find it in your parts book. That flywheel fits a several Chevy models 1966 & up including Camaro, Nova, Chevelle etc. with 350, 396 & 427 cu. in. engines. Diameter is 14" 168 tooth. Uses 11" clutch. This flywheel is correct for internally balanced V-8's as listed above and is not intended for a 454 cu. in. engine.
P/N for Chevy with 11” clutch is 3998281, all except 400 sb and 454. Obviously no longer in GMPD system.